This invention relates to a safety switch for disconnecting both sides of an electrical load in an electrical appliance from the power lines of the appliance thereby to reduce both shock and fire hazards when the appliance is turned off in the event of a short circuit of the load. More specifically, this switch is a combination motor starting switch and load disconnect switch operable by a centrifugal actuator which is typically included in the appliance drive motor.
As is conventional, the wiring system in a house or other building is such that at any outlet, one of the outlet leads is connected directly to the power line coming into the house and the other lead is connected to an electrically grounded return line. Switches for appliances or the like typically operate by making or breaking either the power input lead or the ground lead. In connecting most appliances to a home wiring system, it is difficult to determine which lead is the power input lead and which is the return lead, and many appliances it will operate satisfactorily no matter how the appliance is wired to the input and return leads. In certain instances with the on-off switch of an appliance (for example, the timing switch of an electric clothes dryer or the like) making or breaking the grounded return lead of the appliance, a mechanical or electrical failure of the load could short circuit the load to ground thus creating a shock or fire hazard in the appliance even though the appliance is turned off. This danger is especially apparent in such electrical appliances as electric clothes dryers in which the breakdown of the insulator supporting the heating element, or the breakage or sagging of the heating element wires, could result in a short circuit of the heating element to ground. Further, in such appliances as electric clothes dryers powered by 230 volt current, it will be appreciated that both power input leads are "hot" so that a failure of the heating element could cause a 115 v. short to ground through the element. Heretofore, motor starting switches for the drive motor of the appliance were known which not only effected energization and deenergization of the starting winding of the drive motor upon start up and shut down of the motor, but also, certain of these motor starting switches disconnected one side or the other of an electrical load from one of the power lines of the appliance. However, since only one side of the load was disconnected from the load lines, in many instances the load would still be connected to the power input lead so that in the event of a failure of the load to ground, a short circuit of the load could occur.
Reference may be made to the co-assigned U.S. Pat. No. 4,034,173 which discloses a motor starting switch in the same general field as the switch of this invention and to the co-assigned U.S. patent application Ser. No. 938,455 filed Aug. 30, 1978, now U.S. Pat. No. 4,240,001.